<template>
    <ul class="list">
        <li class="item"
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart.prevent="handleTouchState"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
        >{{item}}</li>
    </ul>
</template>
<script>
export default {
    name:'CityAlphabet',
    data(){
        return{
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated(){
        this.startY=this.$refs['A'][0].offsetTop//获取a元素到顶部的高度
    },
    computed:{
        letters(){
            const letters=[]
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
            // console.log(e.target.innerText)
        },
        handleTouchState(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){//如果你正在做移动手指这件事情我就清除定时器
                   clearTimeout(this.timer) 
                }
                this.timer = setTimeout(()=>{//正在做移动手指16毫秒间隔从新开始定时器
                    const touchY = e.touches[0].clientY-79
                    const index = Math.floor((touchY-this.startY)/20)
                    if(index>= 0 && index<this.letters.length){
                    this.$emit("change",this.letters[index])//返回这个letters字母数组第几项
                    }
                },16)
                
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    },
    props:{
        cities:Object
    }
}
</script>
<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
        display:flex
        flex-direction:column
        justify-content:center
        position:absolute
        top:1.58rem
        right:0
        bottom:0
        width:.4rem
        .item
            line-height:.4rem
            text-align: center
            color:$bgColor
</style>